Jonathan J. Spurgeon

The Global Status of Freshwater Fish Age Validation Studies and a Prioritization Framework for Further Research

Age information derived from calcified structures is commonly used to estimate recruitment, growth, and mortality for fish populations. Validation of daily or annual marks on age structures is often assumed, presumably due to a lack of general knowledge concerning the status of age validation studies. Therefore, the current status of freshwater fish age validation studies was summarized to show where additional effort is needed, and increase the accessibility of validation studies to researchers. In total, 1351 original peer-reviewed articles were reviewed from freshwater systems that studied age in fish. Periodicity and age validation studies were found for 88 freshwater species comprising 21 fish families. The number of age validation studies has increased over the last 30 years following previous calls for more research; however, few species have validated structures spanning all life stages. In addition, few fishes of conservation concern have validated ageing structures. A prioritization framework, using a combination of eight characteristics, is offered to direct future age validation studies and close the validation information gap. Additional study, using the offered prioritization framework, and increased availability of published studies that incorporate uncertainty when presenting research results dealing with age information are needed.

Macroinvertebrate prey availability and food web dynamics of nonnative trout in a Colorado River tributary, Grand Canyon

Abstract: Nonnative fishes have been linked to the decline of native fishes and may affect aquatic food webs through direct and indirect pathways. These concerns have led to efforts to remove nonnative Brown and Rainbow Trout, which are abundant in tributaries of the Colorado River, to enhance native fish communities. We sampled fish, benthic, and drifting macroinvertebrates in November 2010, January 2011, June 2011, and September 2011 to assess resource availability and to evaluate the effects of nonnative Brown and Rainbow Trout in a tributary of the Colorado River in the Grand Canyon. We evaluated trout diets from stomach samples collected during macroinvertebrate sampling periods, and we estimated annual consumption with bioenergetics models. We used 13C and 15N stable isotopes to examine potential diet overlap between native and nonnative fishes. Contributions to benthic biomass varied among megalopterans (16–35%), trichopterans (19–28%), and ephemeropterans (9–32%), whereas ephemeropterans dominated biomass (44–64%) in drift samples. Ephemeropterans were dominant in diets of small (<150 mm total length [TL]) trout, whereas Corydalus and native fish dominated diets of large (>150 mm TL) Brown Trout, and Corydalus and algae dominated diets of large Rainbow Trout. Annual resource consumption was 6× higher for large trout than small trout. Stable isotopes suggested diet overlap between native and nonnative fishes. Large nonnative trout occupied the highest trophic positions. Our results suggest that suppression of nonnative trout may have a positive effect on native fishes via reduced predation and resource competition.

Reservoir Rehabilitations: Seeking the Fountain of Youth

Aging of reservoirs alters the functions, and associated services, of these systems through time. The goal of habitat rehabilitation is often to alter the trajectory of the aging process such that the duration of the desired state is prolonged. There are two important characteristics in alteration of the trajectory—the amplitude relative to current state and the subsequent rate of change, or aging—that ultimately determine the duration of extension for the desired state. Rehabilitation processes largely fall into three main categories: fish community manipulation, water quality manipulation, and physical habitat manipulation. We can slow aging of reservoirs through carefully implemented management actions, perhaps even turning back the hands of time, but we cannot stop aging. We call for new, innovative perspectives that incorporate an understanding of aging processes in all steps of rehabilitation of reservoirs, especially in planning and assessing.

Variability in Age Estimation Results in Ambiguity and False Understanding of Population Persistence

AbstractMortality, growth, and recruitment are the primary dynamic rate functions that regulate fish populations. Age data obtained from calcified structures can provide direct and indirect information needed for calculations of these metrics; therefore, knowledge of the fish population age structure is often coveted information. Unfortunately, potential sources of error exist in the form of subjectivity in interpretation of growth increments, inconsistent deposition of growth increments, and lack of validation in age-estimation processes. However, many sources of error are either not known or simply ignored, particularly for long-lived fishes. Therefore, we included a level of uncertainty in our age estimates of a periodic life history strategist, the Shovelnose Sturgeon Scaphirhynchus platorynchus, by incorporating variability in reader assignment of age. We used a bootstrapping procedure to generate a matrix of new age distributions and demonstrated how calculations of mortality varied as a result of r...

Status of Native Stream Fishes within Selected Protected Areas of the Niobrara River in Western Nebraska

Lotic systems within the Great Plains are characterized by highly fluctuating conditions through both space and time. Fishes inhabiting these systems have adopted specific life-history strategies to survive in such environments; however, anthropogenic disturbance to prairie streams has resulted in declines and extirpation of many native stream fishes. Terrestrial protected areas (i.e., parks and reserves) are designated to support native flora and fauna and, it is assumed, to provide protection to native fishes. We assessed the presence and relative abundance of stream fish populations within protected areas along the Niobrara River in western Nebraska based on data collected during 1979, 1989, 2008, and 2011. The spatial extent of protection, landscape changes resulting in degraded physiochemical parameters, and introduced species may reduce the effectiveness of these terrestrial protected areas in protecting native fishes in Great Plains stream environments.

Using standardized fishery data to inform rehabilitation efforts

Abstract Lakes and reservoirs progress through an aging process often accelerated by human activities, resulting in degradation or loss of ecosystem services. Resource managers thus attempt to slow or reverse the negative effects of aging using a myriad of rehabilitation strategies. Sustained monitoring programs to assess the efficacy of rehabilitation strategies are often limited; however, long-term standardized fishery surveys may be a valuable data source from which to begin evaluation. We present 3 case studies using standardized fishery survey data to assess rehabilitation efforts stemming from the Nebraska Aquatic Habitat Plan, a large-scale program with the mission to rehabilitate waterbodies within the state. The case studies highlight that biotic responses to rehabilitation efforts can be assessed, to an extent, using standardized fishery data; however, there were specific areas where minor increases in effort would clarify the effectiveness of rehabilitation techniques. Management of lakes and reservoirs can be streamlined by maximizing the utility of such datasets to work smarter, not harder. To facilitate such efforts, we stress collecting both biotic (e.g., fish lengths and weight) and abiotic (e.g., dissolved oxygen, pH, and turbidity) data during standardized fishery surveys and designing rehabilitation actions with an appropriate experimental design.